1. Field of the Invention
The present invention generally relates to a compact cellular phone, and more particularly to the compact cellular phone in which a pair of housings formed in an approximate flat shape is foldably connected by using a hinge.
The present application claims priority of Japanese Patent Application No. 2000-366700 filed on Dec. 1, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
As shown in FIG. 1A, in a configuration of a conventional cellular phone, a whip antenna 14 has a ¼ wave length or ½ wave length and is provided to a housing 15. And the whip antenna 14 can be retracted into the housing 15. A coil antenna 16 is wound around dielectrics provided at a top end of the whip antenna 14. When the whip antenna 14 is retracted into the housing 15, the coil antenna 16 remains outside the housing 15 and serves as an antenna for a transmission instead of the whip antenna 14. In addition, a planar inverse F-type antenna (not shown) is provided inside the housing 15. Thus, a diversity antenna system is made up of the whip antenna 14, the coil antenna 16 and the planar inverse F-type antenna, whereby a phasing caused by multiplex wave can be prevented and a preferable transmission feature can be maintained.
Alternatively, instead of using the whip antenna 14 and the coil antenna 16, as shown in FIG. 1A; a cellular phone may include the planar inverse F-type antenna (not shown) or a planar antenna 17 such as a patch antenna inside a housing 18 as shown in FIG. 2A.
Since the cellular phone is generally contacted with a human head to use, a radio wave emitted from the antenna 14, 16, or 17 is partially blocked by the human head which causes a transmission quality to be degraded. Particularly, the whip antenna 14 or the coil antenna 16 has an isotropic directivity in a surface perpendicular to an axis of the whip antenna 14 or the coil antenna 16 as shown in FIG. 1B. Thus, the radio wave is transmitted toward a human body and a transmission efficiency is deteriorated by the blocking of the radio wave by the human head. As a result, the transmission quality is remarkably degraded.
On the other hand, in a surface perpendicular to the planar antenna 17 such as the planar inverse F-type antenna (not shown) or the patch antenna as shown in FIG. 2A, the planar antenna 17 has a directivity having a greater gain in a direction opposite to a ground board as shown in FIG. 2B and a small amount of radio wave transmits to a side of the human head. Thus, a deterioration of the transmission quality affected by the human head can be suppressed to be smaller. However, in a waiting state, the planar antenna 17 having the directivity of the great gain at only one side of the ground board has problems to send or receive the radio wave between the planar antenna 17 and a base station (not shown) located at an opposite side to a direction in which the planar antenna 17 has a greater directivity.
Also, in a case of using the planar antenna 17 alone, when the planar antenna 17 is covered with a hand holding the cellular phone, the transmission effect is remarkably degraded and then a degraded transmission quality disconnects a transmission.
In order to suppress degrading the antenna characteristics affected by the human head and realize a stable transmission, the Japanese Laid-open Patent Application No. Hei 11-220418 discloses an “Outer Antenna Device for Cellular Phone” in which a technology is disclosed to mount the outer antenna at a bottom surface of the cellular phone. However, since another device for the outer antenna is mounted outside the cellular phone, it is cumbersome to handle the entire cellular phone and a device shape becomes large-sized.